Ramjet motor with multi-stage burning



Dec. 7, 1965 F. L. HAAKE 3,221,496

RAMJET MOTOR WITH MULTI-STAGE BURNING Filed June 26, 1962 an; cu m N] INI NI l 1 INVENTOR. FREDERICK L. HAAKE rromvgr United States Patent3,221,46 RAMJET MOTOR WITH MULTl-STAGE EURNENG Frederick L. I-Iaake,1519 Little Farms Road, Oxnard, Calif. Filed June 26, 1962, Ser. No.266,545 8 Claims. (Cl. 6fl--35.6) (Granted under Title 35, U8. Code(1.952), sec. 266) The invention described herein may be manufacturedand used by or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

This invention relates to ram jet motors, and more particularly to suchmotors wherein a multi-stage burning effect is produced in thecombustion chamber to increase the operating efficiency and thrust ofthe motor.

One of the most critical problems involving ram jet motors is to obtainmore complete burning of the fuel to increase the total thrust for agiven amount of propellant. Whether the ram jet motor be operated onsolid or liquid propellant fuels, incomplete combustion occurs 'wheneverthe fuel particles, for one of many reasons, pass through the combustionchamber without burning, or are burned outside the nozzle and thus donot contribute to the engine thrust.

One of the basic causes of incomplete combustion is the absence ofproper mixing between the ram air and the propellant particles. Variousmeans have been devised to improve such mixing, such as installation ofbaflle plates to increase turbulence and the like. In addition,substantial research has been conducted with regard to thecross-sectional grain configuration to control and improve burningefiiciency, and to vary the speed of the ram air which provides theoxidizer to the propellant.

According to the present invention improved burning efiiciency inthe ramjet engine is achieved by providing therein a plurality of differentsize ram air passages for varying the speed of the ram air passingthrough the engine in a prescribed arrangement, such as to provide, ineffect, multi-stage burning areas in the combustion chamber. In otherwords, at least one ram air passage is so dimensioned as to introducelower velocity ram air, and at least one ram air passage has a largerdimension to introduce a higher velocity air, such that respectivecombustion areas or burning zones occur in generally longitudinallydisposed relation within the combustion chamber. This invention isparticularly suitable for use in solid propellant motors. For example,the ram jet motor can be fabricated of a plurality of uniform elongatesolid propellant grains longitudinally arranged together in a bundle toprovide one or more longitudinal passages formed therebetween. Thebundle of grains is supported within the engine casing such that one ormore passages is provided between the bundle of propellant grains andthe motor casing of a different size than the one or more passageswithin the bundle. The slower ram air passing through the smaller airpassages, being at a higher temperature, will create a combustion areaimmediately aft of the burning end of the propellant bundle, whereas theram air passing through the larger passage being at a higher velocitywill create a combustion area further aft in the combustion chamber, orform an extension thereof mixing and burning the unburned propellantparticles passing aft from the previous combustion stage. In order thatthe cross-sectional area of the respective air passages remainsubstantially the same throughout motor burning, the longitudinalsurfaces of the individual grains are restricted to insure anend-burning grain. The aforedescribed arrangement in effect forms atwo-stage combustion effect with additional stages possible by providingadditional passages different sizes.

A propellant motor fabricated of a plurality of simply constructedpropellant grains, which can be identical, provides a convenient methodto build up motors of different sizes, as well as different arrangementsof burning stages by creating passages of various sized andconfigurations. Compared to the complicated cruciforms or star grainconfigurations presently employed in solid propellant motors, the grainsof the instant invention can be circular or non-circular incross-section, and of the same size or differing in size depending onthe desired ram air flow through the various passages, and thusmaterially reducing the cost and complexity of motor fabrication.

One object of this invention is to provide a ram air, reaction typemotor having improved burning efficiency; and a corollary object is toobtain increased burning efficiency by varying the number and/ or sizesof the ram air passages.

Another object is to provide such ram air motor having a solidpropellant motor fabricated of a plurality of uniform grains which canbe assembled in various configurations according to the required numberand arrangement of ram air passages.

A further object is to provide a ram .air motor which is constructed toprovide, in effect, a plurality of longitudinally spaced combustionareas.

Still a further object is to provide a solid propellant motor that canbe inexpensively constructed and which can be fabricated in varioussizes.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

FIG. 1 is a diagrammatic longitudinal sectional view of a ram airmissile having a reaction-type motor, using either liquid or solidpropellant fuels, and employing an arrangement of different sized ramair passages according to the present invention to provide duringoperation respective combustion envelopes defined by broken lines;

FIG. 2 is a diagrammatic view of a solid propellant motor fabricated ofa plurality of identical and irregular shaped propellant grains suitablyarranged according to the teaching of the present invention to provideone central ram air passage and four outer ram air passages of largerdimensions;

FIG. 3 is a similar view as FIG. 2 wherein the propellant grains areidentical but triangular in cross-sectional configuration to provide twocentral ram air passages and four outer ram air passages;

FIG. 4 is a similar view as FIG. 2 wherein the propellant grains areidentical and cylindrical in shape, and arranged to provide a singlecentral ram air passage and four outer ram air passages;

FIG. 5 is a diagrammatic longitudinal sectional view of a ram airmissile employing a solid propellant motor of the type illustrated inFIG. 4 showing the combustion envelopes in broken lines' created by therespective air passages; and

FIG. 6 is a diagrammatic sectional view of a solid propellant motorcomprising a plurality of different sizes of cylindrical propellantgrains arranged to provide another arrangement of ram air passages ofdifferent dimensions.

Referring to the drawing where like reference numerals refer to similarparts throughout the drawing there is shown in FIG. 1 a ram air missile10 comprising generally a cylindrical casing 12 having a nose endprovided with an air diffuser 13 forming with the casing a ram airintake 14, and an aft end provided with a nozzle 16. An end-burningpropellant motor 18 is supported intermediate the casing in spacedrelation thereto by a spider 19 which allows unrestricted flow of ramair. For the general purpose of this invention, motor 18 can be of aliquid propellant type or a solid propellant type, although the conceptis particularly suitable for solid grain propellant motors for reasonshereinafter described. Only one forward spider 19 is used in end-burningtype of solid propellant grains to avoid interference with the burning.A combustion chamber 20 is longitudinally disposed between motor 18 andnozzle 16, the combustion chamber being so longitudinally dimensioned asto ensure adequate mixing volume for the various burning stages that arecaused by the invention motor. As an example of the relative dimensionsof the diameter of the casing with respect to the length of thecombustion chamber, for a casing 8 inches in diameter the length of thecombustion chamber should be in the order of approximately twentyinches. In combined rocket-ram jet motors, the space normally occupiedby the solid propellant rocket motor is particularly suitable as thecombustion chamber of the ram jet motor.

One of the basic concepts of the present invention is to providedifferent sizes of ram air passages 22 and 24 through motor 18 toimprove the burning efliciency in the combustion chamber in thefollowing manner. Air passage 22 may be annular in shape, or segmentedas illustrated in other modifications to be described, and in any eventlarger than central passage 24 so that the rams air velocity in passage22 is greater than the ram air velocity in passage 24. When motor 18 isignited, the ram air in central passage 24 forms a central combustionenvelope or stage generally defined by the broken line 26, which stageis formed in the forward portion of combustion chamber 20. Passage 22being larger than passage 24 presents less friction to the ram air flowtherethrough enabling the ram air in passage 22 to be at a highervelocity and pressure. Any unburned propellant particles from the firststage 26 will be swept further aft and mixed with oxygen by the ram airin passage 22 and ignited in the second stage generally defined by theenvelope 28, which is tubular in configuration. In addition, it is alsobelieved that hot burned propellant particles from the first stage willbe forced aft into the second stage burning area where they will have aneffect of still further increasing the temperature of the ram airtherein to provide additional thrust. Although the first and secondstages 26 and 28, respectively, are illustrated as well defined volumes,it is apparent that such a condition may not actually be so clearlydefined because of turbulent air currents. Under actual operatingconditions the burning stages 26 and 28 will probably not be readilydistinguishable and will probably appear as one combined burning volume.The higher velocity air in passage 22 as it enters the combustionchamber will create a rolling action, represented by arrows 29, toprovide good mixing of the solid propellant particles and oxygen.

It is apparent that the combustion volume caused by the second stageformed aft of the first stage burning volume will increase the totalcombustion volume within combustion chamber 20 to obtain maximum thrustfrom the motor. Obviously, the combustion chamber must be dimensioned tobe capable of accommodating the enlarged combustion volume resultingfrom the use of the instant invention so that substantially allcombustion occurs within the motor and not outside the motor where itprovides no thrust component.

Although inner and outer passages 24 and 22 are illustrated as beingsmaller and larger in cross sectional area, respectively the arrangementcan be reversed as will be hereinafter described in other embodiments ofthe invention.

FIG. 2 is a cross-sectional view of a solid propellant motor 30fabricated of four identical and irregular concavo-convex shapedpropellant grains 32. The longitudinal surfaces of each grain have arestrictive coating, not shown, to ensure only end burning of thepropellant rains. The grains are transversely arranged in the casing inquadrants, with the outer edges contacting the inner casing wall 34 andthe innerends abutting adjacent grains to form four large outer ram airpassages 36 and one small central passage 38. The operation of motor 30is substantially the same as previously described with motor 18 inFIG. 1. Since the solid propellant grains are of the end-burning type,the cross-sectional dimensions of passages 36 and 38 will remainsubstantially constant throughout ram air motor burning.

FIG. 3 is a cross-sectional view of a solid propellant motor 40 formedof six identical end-burning propellant grains 42 triangular incross-section. The grains are arranged with the apexes of four of thegrains contacting the inner casing wall 44 to form four segmental outerram air passages 46, with the remaining two grains arranged base-to-baseto form two central passages 48. Here also, the operation of motor 40 issimilar to motor 18 in FIG. 1 with the exception that two centralburning envelopes may be formed in the combustion chamber, one for eachcentral passage 48, instead of one envelope as in FIG. 1.

FIGS. 4 and 5 illustrate another modification of a propellant motor 50composed of four identical cylindrical grains 52 suitably supported inlongitudinally contiguous relation within casing 54. The centrallongitudinal air passage 56 between the grains is larger than any one ofthe four outer longitudinal air passage 58 formed between adjacent pairsof grains and the inner wall of the casing. As the ram air velocity willbe greater in the larger central air passage 56 than in the smallerouter air passages 58, burning stage 60 formed adjacent the central airpassage 56 will extend further aft in the combustion chamber 62 and formin effect a second burning stage, whereas the burning stages 64 adjacentthe outer air passages 58 form in effect first burning stages. It isapparent that if more smaller passages 58 are desired the number ofgrains can be increased to give the desired result, as in FIG. 6 to bedescribed.

Still another modification of the novel motor is shown in FIG. 6comprising a plurality of different sizes of cylindrical propellantgrains, namely, an outer hollow circular array of smaller identicalgrains 66 supported directly in a casing 68 and forming a plurality ofouter passages 72 therebetween. A plurality of larger size propellantgrains 74 are secured within the circular array of smaller grains toform two inner air passages 76. One satisfactory arrangement of such amotor can consist of approximately ten outer individual grains, and twoinner grains, as illustrated. If desired the circular array of grains 66could be smaller and supported within the casing by spider, much as inFIG. 1, to form one outer annular passage instead of individual outersegmented passages 72.

The instant invention discovers the improved efficiency that can beobtained in a reaction type ram air motor when the motor is providedwith a plurality of ram air passages that vary in size. The radialrelation of the smaller and larger air passages may vary depending onthe desired result. For example, the smaller passage can be centrallylocated and the larger passage outwardly arranged (FIGS. 1, 2 and 3), orin reverse order (FIGS. 4, 5 and 6). A solid propellant motor utilizingthe invent-ion is easily fabricated of small individual propellantgrains which can be all uniform and simple in design as a manufacturingexpedient, although grains of different sizes can be employed to give adesired result. In very large solid propellant motors the advantages ofsimplicity in fabrication, manufacturing and handling as readilyapparent as well as obviating grain fabrication problems. The number,sizes and disposition of the indivdiual grains will depend on the sizeof the motor as well as other factors. Increased burning efficiency inthis type of motor is believed achieved because of the improved mixingof the propellant and the ram air. In

addition, the use of many small air passages decreases the velocity ofthe ram air flowing over the burning surfaces of individual propellantgrains raising the air temperature. Also, the high velocity air in thelarger passage mixes with the low velocity air to form in effect anafter burning stage in the combustion chamber. In other words, theslower ram air passing through the ram jet motor forms a first stageburning while the faster ram air forms a second stage burning. It isapparent that the ram air motors of FIGS. 2 to 6 inclusive can bemounted within the casing, such as in FIG. 1, to provide an outerannular ram air passage.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

I claim:

1. A reaction-type ram air motor comprising (a) a cylindrical motorcasing terminating in a nozzle (b) a solid propellant charge mounted insaid motor casing longitudinally spaced from said nozzle to form acombustion chamber therebetween.

(c) said solid propellant charge being formed of a plurality ofindividual solid propellant grains of the end burning type the toolcross-sectional area of all the grains combined being less than thecrosssectional area of the motor casing, said grains being arrangedtraversely in said casing to provide a plurality of longitudinal ram airpassages leading to the combustion chamber;

(d) at least a portion of said air passages having differentcross-sectional areas to pass ram air at different velocities; said airpassages being open along their entire length throughout operation ofthe motor;

(e) the cross-sectional areas of said air passages remainingsubstantially constant throughout motor combustion (f) the longitudinallength of the combustion chamber being of a dimension as to allow theformation of longitudinally disposed burning zones therein for therespective ram air passages so as to achieve substantially completecombustion in the combustion chamber prior to exhaust through saidnozzle.

2. The ram air motor of claim 1 wherein all of said solid propellantgrains are identical in shape and size.

3. The ram air motor of claim 1 wherein all of said solid propellantgrains are non-cylindrical.

4. The ram air motor of claim 1 wherein all of said solid propellantgrains are cylindrical.

5. The ram air motor of claim 1 wherein the air passages of a smallercross-sectional area are arranged rad-ially outwardly in the casing fromthe air passage having larger cross-sectional area.

6. The ram air motor of claim 1 wherein said solid propellant charge issupported in spaced relation to the inner wall of the motor casing toform an annular ram air passage around said charge.

7. The ram air motor of claim 1 wherein the individual propellant grainsare cylindrical and are traversely arranged peripherally in the .casingwith their adjacent longitudinal surfaces abutting to each other incircular relation and engaging the inner wall of the casing, adjacentpairs of grains forming therebetween and with the casing a longitudinalair passage.

8. A reaction-type ram air motor comprising (a) a cylindrical motorcasing terminating in a nozzle;

(b) a propellant charge mounted in said motor casing longitudinallyspaced from said nozzle to form a combustion chamber therebetween;

(c) said propellant charge arranged in said casing to provide aplurality of longitudinal ram air passages leading to the combustionchamber;

((1) at least a portion of said air passages having differentcross-sectional areas to pass ram air at different velocities; said airpassages being open along their entire length throughout operation ofthe motor;

(e) means for maintaining constant the velocity of the air reaching saidcombustion chamber through the longitudinal ram air passagessubstantially constant throughout motor combustion;

(f) the longitudinal length of the combustion chamber being of adimension greater than the diameter 'of the casing as to allow theformation of longitudinally disposed burning zones therein for therespective ram air passages so as to achieve substantially completecombustion in the combustion chamber prior to exhaust through saidnozzle,

MARK NEWMAN, Primary Examiner. SAMUEL FEINBERG, Examiner.

1. A REACTION-TYPE RAM AIR MOTOR COMPRISING (A) A CYLINDRICAL MOTORCASING TERMINATING IN A NOZZLE (B) A SOLID PROPELLANT CHARGE MOUNTED INSAID MOTOR CASING LONGITUDINALLY SPACED FROM SAID NOZZLE TO FORM ACOMBUSTION CHAMBER THEREBETWEEN. (C) SAID SOLID PROPELLANT CHARGE BEINGFORMED OF A PLURALITY OF INDIVIDUAL SOLID PROPELLANT GRAINS OF THE ENDBURNING TYPE THE TOOL CROSS-SECTIONAL AREA OF ALL THE GRAINS COMBINEDBEING LESS THAN THE CROSSSECTIONAL AREA OF THE MOTOR CASING, SAID GRAINSBEING ARRANGED TRANSVERSELY IN SAID CASING TO PROVIDE A PLURALITY OFLONGITUDINALLY RAM AIR PASSAGES LEADING TO THE COMBUSTION CHAMBER; (D)AT LEAST A PORTION OF SAID AIR PASSAGE HAVING DIFFERENT CROSS-SECTIONALAREAS TO PASS RAM AIR AT DIFFERENT VELOCITIES; SAID AIR PASSAGES BEINGOPEN ALONG THEIR ENTIRE LENGTH THROUGHOUT OPERATION OF THE MOTOR; (E)THE CROSS-SECTIONAL AREAS OF SAID AIR PASSAGES REMAINING SUBSTANTIALLYCONSTANT THROUGHOUT MOTOR COMBUSTION (F) THE LONGITUDINAL LENGTH OF THECOMBUSTION CHAMBER BEING OF A DIMENSION AS TO ALLOW THE FORMATION OFLONGITUDINALLY DISPOSED BURNING ZONES THEREIN FOR THE RESPECTIVE RAM AIRPASSSAGE SO AS TO ACHIEVE SUBSTANTIALLY COMPLETE COMBUSTION IN THECOMBUSTION CHAMBER PRIOR TO EXHAUST THROUGH SAID NOZZLE.